Liquefied petroleum gas (“LPG”) fuel supply systems are known, for example, as shown in U.S. Pat. Nos. 5,291,869; 5,325,838; 5,423,303; 6,216,675; and 6,227,173, which patents are incorporated herein by reference in their entirety. Such systems typically include a number of specialized fuel injectors which receive fuel from a high pressure tank. A fuel rail connected in-line with a series of injectors is often employed to deliver supply fuel to the injectors. In many systems, uninjected fuel is returned to the fuel tank. This is generally done to keep the supply fuel as cool as possible, particularly where it is intended to inject LPG in liquid rather than gaseous form.
One approach to injecting LPG without permitting it to vaporize prior to or during injecting is to pump high volumes of supply and return fuel to the fuel injectors. In this way, the supply fuel spends very little time near the heated engine compartment where it can vaporize. Another approach is to employ a refrigeration cycle as described in those patents identified above. The evaporation of return fuel is used to cool supply fuel, thereby maintaining it in liquid form.
Due to the low evaporation temperature of LPG (i.e., evaporates at minus 40° F.), maintaining LPG in a liquid state can pose various challenges. One such challenge relates to calibration of an LPG injector. For these and other reasons, improvements in calibration systems and methods are desirable.